Carboranes and derivatives thereof have been and are being used as burning rate catalysts for solid propellant compositions. Normal-hexylcarborane and carboranylmethyl, -ethyl or -propyl sulfide are typical carborane derivatives which are catalyst-plasticizer compounds that have been used for high burning rate propellants.
Inorganic and organic iron and iron-containing compounds have also been employed in propellants as burning rate catalysts. Ferrocene and ferrocene derivatives are typical of the organoiron compounds which have been used as burning rate catalysts.
Various theories and proposed mechanisms for the acceleration of propellant burning rates have evolved from experimentation in the field of catalysis. Apparently, the rate-controlling step for uncatalyzed propellant burning rates is determined mainly by the rate at which ammonium perchlorate undergoes decomposition. The burning rates of propellants increase as the particle size of ammonium perchlorate catalyst-plasticizer reduced. Smaller particle sizes facilitate the decomposition rate of ammonium perchlorate.
Very fine particle-sized (e.g. of only a few microns average mean-weight-diameter particle size) ammonium perchlorate in conjunction with catalysts (which have been incorporated in the propellant composition as liquid plasticizers) have been responsible for achieving ultrahigh burning rates for propellant compositions. The use of the liquid-type burning rate catalysts, however, has lead to other problems which include catalyst-plasicizer migration into the liner-insulation system.
The migration of liquid catalysts into the liner-insulation material can be eliminated by the use of a mixed intramolecular perchlorate salt: carboranyldiferrocenylmethyl perchlorate. The salt was disclosed and claimed in my U.S. patent application Ser. No. 120,682, filed Mar. 3, 1971. The activity of the compound is attributed to two different mechanisms for burning rate catalysis plus the oxidizer function which is derived from the perchlorate.
A combination catalyst and oxidizer ingredient which could be used as a replacement for a liquid carborane catalyst-plasticizer, and which could be used as a partial replacement for ammonium perchlorate without reducing the perchlorate ion content in the proellant would be highly desirable, particularly, if the catalyst-oxidizer ingredient is a solid ingredient of low explosive sensitivity and has excellent compatibility with the other propellant ingredients.
Therefore, an object of this invention is to provide a propellant ingredient which serves as a combined catalyst and oxidizer and which includes the carboranyl functional group.
Another object of this invention is to provide a catalyst-oxidizer propellant ingredient which includes the carboranyl catalyst material as the major part of the solid ingredient and which overcomes the problem of catalyst-plasticizer migration into the liner-insulation system.
Still a further object of this invention is to provide an oxidizer-catalyst ingredient which will permit the use of a lesser total amount of catalyst and ammonium perchlorate in a propellant formulation, and thereby permit the use of a larger quantity of binder, and/or fuel, and/or oxidizer in the formulation to yield a propellant of high solids (metallic fuel, inorganic oxidizer) loading without adversely affecting the mechanical properties which is the situation which normally arises when the solids loading of a propellant is increased.